The invention relates to a channel allocation method for a packet network.
FIG. 1 shows the parts of the packet network essential for understanding the invention. Mobile stations MS communicate with base stations BTSn (Base Transceiver Station) over an air interface Um. Base stations are controlled by base station controllers BSC which are connected to mobile switching centres MSC. The subsystem managed by the base station controller BSC, including the base stations controlled by it, is generally referred to as a base station subsystem BSS. The interface between the centre MSC and the base station subsystem BSS is called an A-interface. The part of the mobile communication system on the side of the MSC at the A-interface is known as a network subsystem NSS. Correspondingly, the interface between the base station controller BSC and the base station BTS is called an Abis-interface. The mobile switching centre MSC attends to the switching of incoming and outgoing calls. It carries out similar tasks as the exchange of the public switched telephone network PSTN. In addition, it carries out functions characteristic of mobile telephone traffic only, such as subscriber location management, in co-operation with network subscriber registers of which a visitor location register VLR1 is shown in FIG. 1.
A conventional radio connection used in digital mobile communication systems is circuit-switched, which means that the radio resources allocated to a subscriber are kept allocated to this connection for the duration of the call. Packet radio service GPRS (General Packet Radio Service) is a new service designed for digital mobile communication systems. The packet radio system GPRS designed for the GSM system is described in ETSI recommendations TC-TR-GSM 02.60 and 03.60. The packet radio service of the American D-AMPS system is called CDPD.
By means of a packet radio service, a user of the mobile station MS can be provided with a radio connection which efficiently utilizes radio resources. In a packet-switched connection radio resources are allocated only when speech or data is to be sent. Speech or data is assembled into packets of a specific length. (The last packet of a message can be shorter than the others.) When such a packet has been sent over the air interface Um and the sending party does not immediately have the next packet to send, the radio resource can be released to the use of other subscribers. The packet radio service is particularly suitable for users of data services. This is illustrated by a computer PC in FIG. 1. The computer PC and the mobile station MS can naturally be integrated into a combined unit. Any terminal equipment can be in place of the mobile station MS.
The system of FIG. 1 includes a separate Serving GPRS Support Node, that is, an SGSN, which controls the operation of the packet data service on the network side. This control includes, for example, registrations of the mobile station to the system and from the system (Logon and Logoff, respectively), updating locations of mobile station and routing data packets to the correct destination. In the context of the present application, xe2x80x9cdataxe2x80x9d broadly interpreted refers to any information which is transmitted in a digital mobile communication system and which, in addition to ordinary data transmission, can include a video signal encoded in a digital form, or telefax data. The SGSN may be located in connection with the base station BTS, the base station controller BSC or the mobile switching centre MSC, or it may be located separately from them. The interface between the SGSN and the base station controller BSC is known as a Gb-interface.
The random access method used in the conventional GSM system is explained for example in Moulyxe2x80x94Pautet: The GSM system for Mobile Communications, ISBN 2-9507190-0-7, p. 368 ff. To put it very simply, this random access method broadcasts information about radio channels and their allocation situation. Mobile stations can attempt to reserve a free radio channel. If the base station is successful in decoding exactly one reservation attempt, it responds to the mobile station in question and allocates a radio channel to it. If the mobile station does not get a response, it attempts to reserve again after a random period of time. In a very congested network, it would be possible that most of the reservation attempts would be these re-reservation attempts and only a small portion would be first attempts. In order to avoid this situation, the GSM system has mechanisms for restricting traffic temporarily, such as restricting the number and/or duration of new attempts and closing off one or more access classes. When a radio channel is released, all mobile stations do not automatically attempt to reserve it as this would lead automatically to a congestion in a situation where several mobile stations wait for a radio channel to be released. Instead, the mobile stations determine the probability on which they attempt to reserve at each time slot. The probability may depend on the loading of the base station. This allocation method is known by the general term radio resource allocation.
As in a packet network radio resources can be released after sending of each radio packet, radio resources also have to be allocated separately for the sending of each radio packet. Therefore the packet radio network sets considerably higher demands on the used random access method than a conventional mobile communication system used for speech transmission in which system radio resources are allocated only at the beginning of the call and possibly in connection with a handover.
A partly similar problem as in packet radio networks can be seen in some local area networks, such as Ethernet networks. The solutions of local area networks are not suitable for packet radio networks as all work stations of a local area network are connected to the same cable and they can detect if one work station or more work stations allocate the common resource (in the case of local area network, the network cable). In the packet radio network this is not possible as the mobile station on the side of the cell does not probably hear the transmission of a mobile station on the opposite side of the cell.
A packet radio network can be used in very different applications where speed requirements may vary significantly. For example, International Union of Railways IUR requires that a message of 128 bytes is transmitted in less than 0.5 seconds at the highest priority. Such messages can be used for stopping a train when danger threatens. The transmission of short messages via the packet radio network can be thought to be an example of a less critical application. Short messages can signal an audio message waiting in a voice mail box, for example. Then it is of no great significance if the message was delayed some minutes.
Very different needs can be present even in the same application. For example, when browsing the Internet, it is important that commands of one or a few characters in length are transmitted to the server as fast as possible. On the other hand, response times do not have the same significance in connection with long data transmissions.
The object of the invention is to develop a method for reserving a data transmission channel or its sub-channel in a telecommunication network using radio resource allocation in such a manner that the problems mentioned above can be solved. The objects of the invention are achieved with the method which is characterized by what is stated in claim 1. The dependent claims relate to the preferred embodiments of the invention.
The invention is based on that:
different priorities are assigned to the data packets to be sent;
different priorities are also assigned to possible control sub-channels and the telecommunication controller sends to the terminal equipments information about the priorities assigned to control sub-channels;
on the basis of the priority of the data packet to be sent and the priority of the control sub-channels, each terminal equipment determines the moments when said terminal equipment is allowed to send a channel request.
In the present application, a control sub-channel refers to a channel which the mobile station or some other terminal equipment uses for sending a channel request of a transmission channel. A priority class refers to the terminal equipments or application to the data packets of which the same priority is assigned.
The advantages of the method of the invention are e.g. a good response time for packets with a high priority and equability for each priority class. The specific advantages of the preferred embodiments of the invention appear in connection with the embodiments in question.